Strip rolling mill system and process



N. H. POLAKOWSKI 3,344,637 STRIP ROLLING MILL SYSTEM AND PROCESSFiled'Fb. 1, 1965 i 5 QM m w NM. a E V Wm. M H w $9M 7% u 8 W E 1:1 1 SI 3 i: .q 5

United States Patent 3,344,637 STRIP ROLLING MILL SYSTEM AND PROCESSNatalis H. Polakowski, 500 Kin Court, Wilmette, Ill. 60091 Filed Feb. 1,1965, Ser. No. 429,352 8 Claims. (Cl. 7264) ABSTRACT OF THE DISCLOSUREThe invention is addressed to a mill for rolling metal sheets, stripsand the like wherein the metal is passed between reducing rolls fordecreasing its thickness and in which the improvement is addressed tomeans adapted to twist the sheet or strip relative to the rolling planeselectively to increase the tension along the lateral edges of the metalfor corresponding increase in elongation to offset the over-rolling atthe center of the strip by the reducing rolls whereby a more uniformrolled product will result and in which the twisting means comprises thecombination of aligned deflector rolls contacted by one surface of themetal and a flexing roll adapted to contact the opposite surface of themetal between the deflector rolls and means for adjustment of theflexing roll relative to the rolling plane of the metal.

This invention relates to an integrated equipment system and processingmethod for the rolling of metal in strip form. Its purpose is to secureproducts such as sheet, strip or foil of improved flatness compared withwhat can be achieved with conventional rolling mills and methods.

It has been recognized that difliculties in obtaining satisfactoryflatness in these products originate in the rolling operation itself.Both the distance between the work rolls and their deflections vary inthe course of a rolling pass due to slight changes in the incoming stripthickness and hardness, friction between the rolls and work, as well asroll temperature and wear. Each and any of these factors result invariations of roll pressure and, ultimately, of the shape and flatnessof the strip. Because of the random nature of these variations, thecontrol of flatness in the rolling of metal strip always represented aproblem, its severity increasing with decreasing metal thickness.

In many cases, especially on light gauge strip, accepta- 'ble flatnessof the as-rolled metal cannot be attained at all and it is necessary toemploy special corrective devices, such as roller levelers or skin passmills subsequent to the principal reduction-rolling operation. Thesedevices entail a separate operation but their effectiveness is limited,especially on thin strip. In addition, levelers tend to impair thefinish (reflectivity) of bright rolled material while the cost oftempering mills for strip is high. Furthermore, even when an applicationof these corrective devices is contemplated, their task is renderedeasier and more effective when the out-of-flatness of the cold reducedstrip is as small as possible.

As an alternative, or a co-measure with the corrective means discussedabove, certain camber controlling devices involving bending of the workrolls or the backing rolls are increasingly used to compensate forvariable roll deflection, wear, and non-uniform thermal dilatation.Among these devices, those based on bending the work rolls by loadingtheir chocks with the aid of hydraulic cylinders have a small correctiveeffect because of journal pressure limitation. Those based on directbending of the backing rolls are very expensive and unsuitable formounting on existing, conventional rolling mills.

It is an object of this invention to provide a system for the rolling offlat products in continuous lengths (coil stock) which includes meansfor satisfactory, eflicient, and economical control of strip flatness.

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It is a further object of this invention to provide a flatness controlconstruction and principle which can be incorporated into an existingstrip rolling mill irrespective of the design of the rolling stand (orstands) and without making any structural changes thereto.

These and other objects of this invention will appear hereinafter andfor purposes of illustration but not of limitation, specific embodimentsof this invention are shown in the accompanying drawings in which:

FIGURE 1 is a schematic illustration of a rolling mill system includingthe operating mechanisms of this invention;

FIGURE 2 is a view of the system of FIGURE 1 taken about the line 22;and,

FIGURE 3 is a schematic illustration of a modified form of theinvention.

The construction of this invention generally comprises means fortwisting the span of the metal strip between the payoff reel and therolling stand relative to the pass plane while said strip is undertension. The twisting action, which will be described in detailhereinafter, redistributes the total tension by transferring a largerproportion thereof onto the side, or edge portions of the strip whilerelieving it in the center part. Simultaneously, said strip is flexed byrunning it over a small diameter roller and it undergoes a plasticextension (stretch), said extension being substantially proportional tothe tension per square inch for any fixed flexing roller diameter.

By controlling the amount of twist, a preferential extension of the edgeregions is thus obtained, this extension being then used to compensatefor the extra extension of the center of the metal strip caused by heatcamber on the reducing rolls in the mill stand, The construction of thisinvention is capable of providing a more uniform rolled product byreason of this compensation of extensions across the strip.

FIGURE 1 illustrates a rolling stand with work rolls 1 and 2 and backingrolls 3 and 4. It will be understood that the mill for reducing of themetal may be of any conventional type and that the arrangementillustrated is only one typical example.

Located in front of the-reducing rolls is a strip flexing assemblyincluding backup roll 5, deflector rolls 6 and 7 and flexing roll 8. Thegeneral arrangement illustrated is of the same type as the arrangementshown in FIGURE 2 of applicants copending application Ser. No. 390,167,now Patent No. 3,270,543. In the ordinary use of a structure of thisnature, the metal to be flexed is passed in contact with the roll 6,then over flexing roll 8 and finally in contact with deflector roll 7.The flexing roll 8 is of a small diameter so that a significant plasticstrain in the strip and a substantial angle of flexural contact isachieved. Backup roll 5 supports roll 8 against bending.

The illustrated system also includes takeup reel 9*, payoff reel 10 andidler rollers 11 and 12. These last mentioned portions of the describedsystem are considered conventional and various other well-knownarrangements for handling of the strip 13 are contemplated for use inthe system of this invention.

FIGURE 2 illustrates the manner in which the deflector rolls 6 and 7,flexing roll 8 and backup roll 5 are mounted. It will be noted thatcommon journals 14 and 14 are provided for the rolls 5, 6 and 7.Furthermore, these provide for vertical movement of the journals so thatthe angle of the rolls 5, 6 and 7 can be changed relative to thereducing rolls 3 and 4.

In the operation of the instant invention, the strip 13 is passed fromthe payoff reel 10 over the idler 12 and then through the flexingcluster of rolls 5, 6, 7 and 8. With this cluster inclined at an angleas illustrated in the drawings, the strip will be twisted relative toits position as it passes through rolls 1 and 2.

The strip is normally under tension during its traverse prior to entrybetween the reducing rolls; however, with the amount of back tensionnormally used, there will be little perceptible elongation in the strip.When the cluster of rolls 5, 6, 7 and 8 is tilted as described herein,tensions are built-up in the edges of the strip, and these tensions aresubstantially greater than the average tensions in the strip.Accordingly, due to combined action of tension and flexure, the edges ofthe strip will elongate prior to entering the work rolls bight, and theamount of this extension can be controlled by varying the tilt. When thestrip reaches the work rolls, there is a tendency for greater pressureto be exerted upon its center portions because of the pre-ground camberand the thermal camber so that the center obtains a greater extension.

Such condition of over-rolling the center can also arise in conventionalrolling operations when a strip with a full center is reduced betweenwork rolls which do not have a sufficient effective negative camberwhile in operation. Under these conditions, a center-buckled strip willresult. Accordingly, with the cluster 5, 6, 7 and 8 in an inclinedposition, there will be a tendency for the elongation of the strip toequalize since the extra elongation in the center portions will tendtooffset the elongation already produced in the peripheral portions ofthe strip by the described twisting action. It will be appreciated thatthe degree of twisting can be readily controlled with the arrangement ofthis invention and, therefore, adjustments can be made to bring thetotal elongation across the width of the strip to a substantiallyuniform level.

In a typical use of the instant invention, the combination 5, 6, 7 and 8can be associated with a rolling stand having work rolls 1 and 2 whichare ground to produce flat strip when the rolls are cold. As a rollingoperation progresses, the rolls 1 and 2 will begin to swell at thecenter and, therefore, there will be a tendency for the strip toelongate preferentially in the center area. By adjusting the tilt of therolls 5, 6, 7 and 8 as the warming of the work rolls progresses, theedges of the strip can be pre-stretched to compensate for the excessiveelongation which will take place at the center of the strip as it passesthrough the work rolls.

Although the aforesaid operation could be performed after the strippasses through the work rolls, it is preferred to provide forpre-stretching since the appearance (brightness) of the sheet will bemore uniform when all of the compensating extension is introduced beforeor during contact with the work rolls. Furthermore, the prestretchingtakes place in a low tension location since the front tension betweenthe mill and the takeup reel 9 is normally much higher than the backtension. The prestretching, therefore, minimizes any likelihood oftearing of the strip.

By providing an independent adjustment for the backup roll 5, it ispossible to accommodate a wide variety of strip thicknesses. It will beappreciated that various conventional means may be employed forsupporting of the backup roll relative to the deflector rolls 6 and 7.

As shown in FIGURE 1, the twisting action is transmitted to the workrolls 1 and 2 and to reel 10. This may cause the strip to slightly driftsidewise. To prevent this, it may be advantageous to install twoparallel guiding strands, as shown in FIGURE 3, having rolls 31-32 and33-34, respectively. These guiding devices are not driven (idlers), andtheir rolls are spaced apart sufficiently to engage the strip withoutrolling it. The twisting action is then confined to the metal spanbetween the two guide stands and will not affect the coil or work rolls.

From consideration of FIGURES 1 and 3, it follows that the maximumextension of the edges in a strip of a given width is limited by themaximum tilt of the roll cluster in the pre-stretching deviceillustrated in FIG- URE 2 and the distance (free span) between idler 12and work rolls 1-2 in the arrangement in FIGURE 1, or between guidestands 31-32 and 33-34 in FIGURE 3. The shorter the free span and thewider the strip, the less tilt is needed to accomplish a specifiedelongation of the edges. For maximum response per angular unit of tilt,it is thus advantageous to keep this span short. For this reason, anarrangement of the type in FIGURE 3 is preferable to that in FIGURE 1,for the former renders the effectiveness of the system independent fromthe distance between the mill, idler roller, and reel. It is also seenthat presence of the guide stands makes idler roll 12 redundant.

It is also contemplated that the selective increase in tension in thelateral edges of the strip can be accomplished solely due to thetwisting action which is achieved. The twisting action will producesufficient increase in tension to compensate for elongation in thecenter of the strip during working where such elongation is of arelatively low magnitude.

The small diameter flexing roll is preferably utilized in this inventionsince this roll will, in itself, produce plastic strain in the strip.Obviously, the smaller the diameter of the roll 8, the less tension willbe needed to differentially stretch the strip. Where relatively greatelongation is anticipated at the center of the metal during reduction ofthe metal by the reducing rolls, a greater compensating extension of thelateral edga can be achieved by the combination of a small diameterflexing roll and the twisting action. A strip twisting action alone canbe employed for small corrections, but it is dangerous beyond a certainpoint since the tension in the edges produced by twisting may reach alevel which would cause tearing in the lateral edges. Where the smalldiameter flexing roll is employed, the diameters preferably extendbetween about inch and /1 inch for strips from 0.002 to 0.025 inchthick.

The arrangement of this invention can be employed in combination with areversing mill by providing one twisting means on either side of themill. The twisting means on the forward side of the mill can be madeinoperative by removing the roll 8 or by opening the gap between therolls by moving backup roll 5 away from rolls 6 and 7.

The flexing roll 8 is preferably a floating roll with its sole supportbeing provided by the backup roll 5 and without the ends being confinedagainst movement in the rolling direction by a fixed journal housing.However, other strip flexing devices can be used for the same purposeand with the same over-all effect, provided they incorporate the lateraltilting principle described herein.

It will be understood that various changes and modifications may be madein the above described construction which provide the characteristics ofthis invention without departing from the spirit thereof particularly asdefined in the following claims.

That which is claimed is:

1. In a rolling mill operation for rolling of metal sheet, strip and thelike wherein the metal is passed between reducing rolls for decreasingits thickness, the improvement comprising means adapted to twist saidmetal relative to the rolling plane for selectively increasing thetension of the lateral edges of the metal to increase the elongation insaid edges and thereby offset the over-rolling of the center of thestrip by the reducing rolls whereby a more uniform rolled product willresult, in which said twisting means comprise the combination of a pairof aligned deflector rolls adapted to contact one surface of said metal,a flexing roll situated between said deflector rolls and adapted tocontact the other surface of said metal whereby said metal is flexedwhen passing over said rolls, and a backup roll for said flexing roll.

2. A rolling mill in accordance with claim 1 wherein said means fortwisting of the metal is located between said reducing rolls and apayofi reel for said metal.

3. A rolling mill in accordance with claim 1 comprising a reversingmill, one of said twisting means being located on either side of saidreversing mill for individually handlng said metal depending on thedirection of operation of said mill, and means for making one of saidtwisting means inoperative while the other twisting means handles saidmetal.

4. A rolling mill in accordance with claim 1 including means foradjusting the degree of twisting action of said twisting means.

5. A rolling mill in accordance with claim 4 wherein said backup rolland said deflector rolls are supported in common mountings and includingmeans associated with said mounting means for adjusting the angle ofdisposition of said backup and deflector rolls to thereby adjust thetwisting eifect of said rolls.

6. In a rolling mill operation for the rolling of metal sheet, strip andthe like wherein said metal is passed between reducing rolls fordecreasing its thickness, the improvement comprising means adapted totwist said metal relative to the rolling plane for selectivelyincreasing the tension in the lateral edges of the metal, and a smalldiameter flexing roll associated with said twisting means whereby theelongation of said strip in said edges is increased to thereby offsetthe over-rolling of the center of the strip by the reducing rolls toachieve a more uniform rolled product.

7. A rolling mill in accordance with claim 6 wherein said flexing rollhas a diameter between 0.2 and 0.75 inch.

8. In a method for the rolling of metal wherein the metal is to bepassed between reducing rolls for decreasing its thickness, theimprovement comprising simultaneously passing said metal over a smalldiameter flexing roll and twisting said metal relative to the rollingplane when passing through said reducing rolls, and whereby tension isintroduced in the lateral edges of the metal to offset the stressesintroduced at the center of the metal by the reducing rolls to achieve amore uniform rolled product.

References Cited UNITED STATES PATENTS 6/ 1962 Lasiewicz et al 72164 3/1963 Roberts 72-9

1. IN A ROLLING MILL OPERATION FOR ROLLING OF METAL SHEET, STRIP AND THELIKE WHEREIN THE METAL IS PASSED BETWEEN REDUCING ROLLS FOR DECREASINGITS THICKNESS, THE IMPROVEMENT COMPRISING MEANS ADAPTED TO TWIST SAIDMETAL RELATIVE TO THE ROLLING PLANE FOR SELECTIVELY INCREASING THETENSION OF THE LATERAL EDGES OF THE METAL TO INCREASE THE ELONGATION INSAID EDGES AND THEREBY OFFSET THE OVER-ROLLING OF THE CENTER OF THESTRIP BY THE REDUCING ROLLS WHEREBY A MORE UNIFORM ROLLED PRODUCT WILLRESULT, IN WHICH SAID TWISTING MEANS COMPRISE THE COMBINATION OF A PAIROF ALIGNED DEFLECTOR ROLLS ADAPTED TO CONTACT ONE SURFACE OF SAID METAL,A FLEXING ROLL SITUATED BETWEEN SAID DEFLECTOR ROLLS AND ADAPTED TOCONTACT THE OTHER SURFACE OF SAID METAL WHEREBY SAID METAL IS FLEXEDWHEN PASSING OVER SAID ROLLS, AND A BACK UP ROLL FOR SAID FLEXING ROLL.